Active bolster vent distribution for stress and load management

ABSTRACT

An active bolster mounts at an interior trim surface of a passenger compartment in an automotive vehicle. A plastic-molded front wall deploys in a deployment direction toward a passenger in the passenger compartment. A plastic-molded bladder member is joined along an outer perimeter with the front wall by a hot weld seam to form an inflatable bladder. The bladder member includes at least one substantially circumferential pleated baffle. An inflator couples an inflation gas into the inflatable bladder in response to a crash event of the vehicle. The pleated baffle forms a plurality of at least five vent openings including at least one stress relief vent juxtaposed to a peak stress region of the hot weld seam and a plurality of tuning vents which are concentrated at a lowest restraint-force region of the inflatable bladder.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application based on co-pending U.S. applicationSer. No. 14/659,724, filed Mar. 17, 2015, which is incorporated byreference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

BACKGROUND OF THE INVENTION

The present invention relates in general to active bolsters for occupantcrash protection in automotive vehicles, and, more specifically, to anactive bolster with an inflatable bladder formed by plastic wall panelsthat is vented for a controlled release of inflation gas to reduce peakstresses on a weld seam between the panels and to tune restraint forcesprovided at different locations of the bolster.

An active bolster is a vehicle occupant protection device with agas-inflatable bladder to absorb impacts and reduce trauma to occupantsduring a crash. As opposed to deployable air bag cushions made ofvarious fabrics that emerge from behind various openings upon inflation,active bolsters use the interior trim surface itself to expand at thebeginning of a crash event for absorbing the impact and dissipatingenergy through the action of an inflation gas. U.S. Pat. No. 8, 205,909,issued Jun. 26, 2012, incorporated herein by reference, discloses anactive knee bolster integrated into a glove box door that is lightweight and visually attractive. U.S. Pat. No. 8,474,868, issued Jul. 2,2013, also incorporated herein by reference, discloses a typicalstructure wherein an active bolster includes a front wall or trim panelthat faces a vehicle occupant attached to a back wall or bladder memberalong a sealed periphery. One or both of the walls is deformable inorder to provide an expandable, inflatable bladder. For example, thebladder member may have a pleated (i.e., accordion-like) region thatstraightens out during inflation. The walls are initially spaced apartby a small amount when in their pre-deployment, non-inflated condition.This allows ingress of the inflation gas in a manner that achieves aneven inflation across the panel.

The front and back walls of a typical bladder for an active bolster arecomprised of molded thermoplastics such as polyethylene, polyolefin, orPVC. They are typically injection molded but can also be blow molded.When formed separately, the front and back walls must be hermeticallyjoined around their periphery in order to form the inflatable bladder.The joint must be strong to resist separation that could result fromhigh inflation pressures during inflation and that result when apassenger impacts the bolster. The peripheral seal is formed by hotwelding, for example.

It is known that in order to optimize the dissipation of energy when anoccupant contacts an air bag or an active bolster, inflation gas shouldbe vented to allow a controlled collapse of the airbag that safelydecelerates the impacting occupant. U.S. Pat. No. 8,720,943, issued May13, 2014, which is incorporated herein by reference, discloses an activevent structure for providing a variable vent flow rate. A vent windowformed within the pleated baffle region includes a flap that deflects inresponse to gas pressure to provide a variable window opening.

Various types of structures and locations have been disclosed forventing inflation gas during inflation and during loading by animpacting passenger. Venting locations have been disclosed on thecentral, flat areas of the bladder wall facing the front wall, in thepleated baffle region of the bladder wall, and in welding towers thatattach the bladder wall to a reaction surface, for example. It has beensuggested that an active vent can be placed in close proximity to localregions where the stresses of inflation forces may create a highestprobability of weld failure. However, the placement and relativecapacities of vents can provide additional improvements in stressmanagement and tuning of restraint forces than has been realized in theart.

SUMMARY OF THE INVENTION

In one aspect of the invention, an active bolster mounts at an interiortrim surface of a passenger compartment in an automotive vehicle. Aplastic-molded front wall deploys in a deployment direction toward apassenger in the passenger compartment. A plastic-molded bladder memberis joined along an outer perimeter with the front wall by a hot weldseam to form an inflatable bladder. The bladder member includes at leastone substantially circumferential pleated baffle. An inflator couples aninflation gas into the inflatable bladder in response to a crash eventof the vehicle. The pleated baffle forms a plurality of at least fivevent openings including at least one stress relief vent juxtaposed to apeak stress region of the hot weld seam and a plurality of tuning ventswhich are concentrated at a lowest restraint-force region of theinflatable bladder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an outward-looking, exploded perspective view of an activeknee bolster glove box door system of a type to which the presentinvention can be applied.

FIG. 2 is a rear perspective view of an inflatable bladder assembly ofan active bolster.

FIG. 3 is a side cross section showing a prior art active bolsterassembly.

FIG. 4 is a rear, plan view of a bladder member without vent openings.

FIG. 5 is a rear, plan view of a bladder member with initial placementof stress relief vents according to one embodiment of the presentinvention.

FIG. 6 is a rear, plan view of a bladder member with initial placementof tuning vents according to one embodiment of the present invention.

FIG. 7 is a diagram showing arc sections for defining a minimum spacingbetween vent openings.

FIG. 8 is a diagram showing developmental testing of an active bolsterfor fine tuning of the vent openings.

FIG. 9 is a plot showing actual and desired restrain forces from theactive bolster.

FIG. 10 is rear, plan view of a bladder member with adjusted sizing ofthe tuning vents after prototype testing.

FIG. 11 is a flowchart showing one preferred embodiment of theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to FIG. 1, a prior art active knee bolster system 10 has abase panel component 11 which forms the foundation for the bolster. Base11 may be either attached to the vehicle by hinging from a storagecavity or glove box 12 as shown in FIG. 1, or mounted to anotherstructure such as an instrument panel support located below a steeringcolumn, for example. Such locations are accessible to the knees of anindividual passenger riding in a corresponding seating position within avehicle.

In this embodiment, base 11 is a door inner wall or liner that acts as areaction surface for supporting an inflatable bladder formed by a back(bladder) wall 13 and a front (trim) wall 14 that are joined aroundtheir periphery 15. Walls 13 and 14 are preferably comprised of moldedplastics (such as thermoplastic polyolefin (TPO)) and are joined byplastic hot welding, such as hot plate or vibration welding, to form aperipheral seal around a central region 17 for forming an inflatablebladder. An inflation gas source 16 is electronically controlled foractivating during a crash to release gas to inflate the bolster. Frontwall 14 may comprise the Class A interior trim surface such as theoutside of the glove box door, or an additional skin or cover (notshown) can be applied to its outer surface.

FIG. 2 is a rear view of an inflatable bladder 20 for an active bolster.A plastic-molded front wall 21 overlies a plastic-molded, expandableback wall or bladder member 22. Wall 21 and bladder member 22 are joinedaround a closed perimeter region 23 to form an inflatable bladder havingan open central volume between wall 21 and bladder member 22 to receivean inflation gas from an inflator 24 mounted in a recess 25 of bladdermember 22 during a crash event. Bladder member 22 includes a pluralityof pleats, such as 26 and 27, to accommodate the expansion of bladdermember 22 during inflation. A plurality of attachment towers (i.e.,bosses) 28 project from a central region of bladder member 22 disposedwithin baffle pleats 26 and 27. Towers 28 are used to mount bladdermember 22 to a reaction surface (not shown). Vent holes 30 comprised ofan asterisk-shaped pattern cut through bladder member 22 to vent thebladder chamber.

FIG. 3 shows a cross-section of bladder 20 assembled to a reaction wall34. Baffle pleat 27 is penetrated by a window opening 33 to provide avent. During deployment as a result of an inflation gas being suppliedinto a bladder cavity 36, front trim wall 21 deploys in a deploymentdirection 35 toward a passenger in the passenger compartment of avehicle.

FIG. 4 shows a bladder member 40 with a peripheral welding flange 41along a circumferential edge of bladder member 40. A pleated baffleincludes a pleat 42 circumferentially disposed within welding flange 41which unfolds during bolster deployment. In the preferred embodiment,all the vent openings are formed in pleat 42 since close proximity tothe hot weld seam provides a better ability to reduce stress on theweld.

The size and peripheral locations of the vent openings are driven by twoseparate factors, namely i) creation of stress relief at a peak stressregion of the hot weld seam and ii) tuning of restraint forces acrossthe bladder to provide the desired restraint interaction with animpacting passenger. In regard to stress relief, peak stress regions ofthe hot weld seam are determined that would occur in the absence of anysignificant venting. A typical active bolster has an elongated shapeextending horizontally in a vehicle, as shown in FIG. 4. Stressoccurring along the weld seam as the bladder inflates and then receivesan impact is modeled using computer aided engineering (CAE) tools aspart of the conventional design process utilized by engineers. Mosttypically, the peak stresses occurs along the longest straight sides ofa weld seam, such as shown at regions A and B of the weld seam in FIG.4.

Intended variations of the restraint force created across an activebolster may result from an overall restraint strategy for a particularvehicle in view of many factors such as relative passenger positioningand the influence of other restraint devices. Target values fordeflection forces provided at different regions of an active bolsterwould generally be determined by a design group handling thesafety/restraints specifications for a vehicle design. For example, itis often desirable that a left or right side of an active bolsterprovide greater restraint force than the other. In the case of an activebolster incorporated in a glove box door, a sweeping (i.e., angled)surface of the instrument panel/glove box combination may place oneparticular side of the active bolster closer to the passenger than theother side. In order to obtain equal loading against the left and rightknees of the passenger during an impact, the closest side of the activebolster should provide a lower restraint force to the correspondingknee. In the example of FIG. 4, a region C corresponds to a lowestrestraint force region because it interacts with a passenger's leftknee. As described below, a concentration of vent openings correspondingto a lowest restraint force region achieves a desired reduction in kneerestraint-force loading as a result of a corresponding local increase inventing.

As shown in FIG. 5, the invention first places a stress relief vent 43juxtaposed with peak stress region A of the hot weld seam. In the eventthat a particular design is found to have additional high stressregions, then more than one relief vent may be used. For example, asecond stress relief vent 44 is juxtaposed with peak stress region B.More than two vents can be utilized if additional high stress regionsare identified using CAE analysis. Preferably, the stress relief ventshave a fixed first aperture area which is relatively large (compared tothe tuning vents to be described next) in order to provide sufficientstress relief for the weld seam. In addition, the total area (i.e,cross-sectional flow capacity) provided by the stress relief vents isselected to be somewhat less than the total venting capacity thatcorresponds to the desired level of impact energy absorption specifiedfor the active bolster. This reserves an additional flow capacity to beprovided by the tuning vents. Stress relief vents 43 and 44 may haveslotted shape as shown, or may be circular. The first aperture area maytypically correspond to that of a 10 mm diameter hole, for example.

As shown in FIG. 6, the invention places a plurality of tuning ventsalong pleat 42 so that the tuning vents are concentrated at lowestrestraint-force region C. Thus, tuning vents 45-49 have been placed inpleat 42 along the right side edge of FIG. 6, which corresponds to theleft knee of the passenger when bladder member 40 is assembled into aglove box door (not shown). To maintain sufficient impact energyabsorption/deflection around the entire hot weld seam, additional tuningvents 50 and 51 are placed along the left side of FIG. 6. Preferably,vent openings (including both stress relief vents and tuning vents) aredistributed along the outer perimeter of bladder member 40 such thatevery possible rotational position of a 90° are along peripheral weldingflange 41 includes at least one vent opening. In one preferredembodiment, an initial size for each tuning vent 45-51 has a fixedaperture area that is determined according to the smallest hole that canbe reliably formed by the injection molding process that is used tofabricate bladder member 40 (e.g., about 3 mm) Based on the size andnumber of tuning vents, the total venting capacity based upon theinitial configuration of both stress relief and tuning vents shown inFIG. 6 may be less than the total desired venting capacity so thatmodifications to the relative restraint force provided across bladdermember 40 can be adjusted by changing (i.e., increasing) the aperturearea of various vent openings as described below.

In order to avoid stress imbalances and overly large differences ofrestraint force deflection between different sections of the activebolster, present invention may employ a vent spacing requirement whichavoids any long sections of the weld seam without any vent opening. Asshown in FIG. 7, the closed-loop path of a hot weld seam 55 extendsaround a center 57 and along a periphery of a bladder member. Aplurality of vent opening locations 56 are distributed around the path.As an arc of a predetermined angular size is rotated around center 57, avent opening is always present. For example, an arc 58 spanning 90°between a radial line 59 and a radial line 60 includes one vent opening.Rotating the arc to a position 61 between radial lines 62 and 63 resultsin three included vent openings as a result of a concentration of tuningvents. By ensuring that adjacent vent openings are separated by no morethan the predetermined arc size, subsequent adjustment of the restraintforces at any section of the bladder can be fine tuned as describedbelow.

In order to conform the inflation and impact performance of the activebolster to the desired performance determined by the designspecifications, physical prototypes using a bladder member having theinitial vent opening sizes and locations are crash tested as shown inFIG. 8. Thus, an instrument panel 64 with an active glove box bolster 65is arranged in a test setup which may include a prototype or simulatedpassenger compartment with a passenger seat 66. During testing tosimulate an impact, the active bolster deploys to a position 68 toreceive an impact with a crash dummy 67 which includes sensors connectedto a data collection/processor device 70. The sensors measure in actualrestraint profile (i.e., restraint force generation during a crash eventat different locations on the active bolster) obtained with the initialplacement and size of the vent openings. The actual restraint profilemay be compared with the desired restraint profile to identifymismatches where the bolster is providing greater than the desiredamount of restraint force. In response to any mismatches, selected ventopenings nearest the areas of mismatch may have their initial apertureareas increased, thereby reducing the restraint force provided in thecorresponding area and reducing the mismatch.

FIG. 9 depicts a desired restraint profile 75 in which the desiredmagnitude of the restraint/deflection force varies according toleft/right horizontal position across the active bolster. Line 76represents an actual restraint profile as measured from prototypetesting. Positions on the active bolster where line 76 is greater thanline 75 are used to identify locations along the weld seam where theincluded vent openings are increased. Since the aperture sizes areadjusted and no changes in the positions of vent openings is necessary,the prototype tooling developed for the bladder member can be easilyadapted and used for final production. Using an iterative process of CAEanalysis and prototype testing, final aperture sizes for tuning vents45-51 are determined as shown in FIG. 10.

A method for configuring vent openings in an active bolster is shown ingreater detail in FIG. 11. During initial vehicle development in step80, a vehicle design team lays out a passenger compartment, interiortrim surfaces, passenger seating, and restraint target specifications asknown in the art. In step 81, an active bolster is designed inaccordance with the vehicle specifications, including the determinationof the shapes for the bladder member and front trim wall, the materialsto be used, inflator design, and the basic manufacturing processes toproduce the active bolster. For example, the size and number of pleatsin the pleated baffle corresponds to a desired expansion shape of thebladder member based on the expansion distance and an angled sweep of aninstrument panel or glove box door with respect to a passenger seat(which places one side of the active bolster closer to the knees of thepassenger than the other side).

In step 82, a CAE model of the active bolster is developed in order tomodel deployment of the bolster, the weld stress, and the restraintforces. In step 83, high stress regions are identified along the hotweld seam (wherein modeling is based on less than full venting). Usingless than full venting helps to identify the regions of high stress. Atleast initially, the CAE modeling may assume no venting at all.Alternatively, high stress regions can be identified without CAEmodeling, such as by associating the longest straight sides with a highstress region.

In step 84, low restraint-force regions are identified along the bolsterin response to a desired restraint profile specified by asafety/restraint design group responsible for modeling impact forcesduring various vehicle crashes (e.g., using corresponding CAE or othertools known in the art).

Based on the locations of high stress regions and low restraint-forceregions, the method proceeds in step 85 to place stress relief ventsproximate to the high stress regions. In step 86, tuning vents areplaced so they are concentrated at the low restraint-force region(s).Preferably, the stress relief vent(s) have a first aperture area whichhas in initial value greater than the smallest manufacturable sizeobtained with the injection molding process and tools being used. Eachof the tuning events has an initial aperture area less than the firstaperture area and preferably equal to a smallest manufacturable size. Inaddition, a vent spacing is maintained such that an arcuate distancebetween adjacent vent openings is less than 90° (which means that thetotal number of vent openings is greater than or equal to five).

In step 87, a prototype active bolster is built and tested (with theinitial and/or intermediate, modified aperture areas for the ventopenings). During crash testing, profiles for the actual restraintforces/deflection are collected. In step 88, the actual restraintprofiles are compared with the desired restraint profile (i.e., target).Based on differences between the actual and desired restraint profiles,selected tuning vents are enlarged in step 89 so that the targetrestraint characteristics are obtained.

What is claimed is:
 1. A method of configuring inflation of an activebolster for mounting at an interior trim surface of a passengercompartment in an automotive vehicle, wherein the bolster comprises aplastic-molded front trim wall for deploying in a deployment directiontoward a passenger in the passenger compartment, a plastic-moldedbladder member joined along an outer perimeter with the trim wall by ahot weld seam to form an inflatable bladder wherein the bladder memberincludes at least one substantially circumferential pleated baffle, andan inflator for coupling an inflation gas into the inflatable bladder inresponse to a crash event of the vehicle, the method comprising thesteps of: configuring the shapes of the trim wall and bladder member tomeet specifications for the automotive vehicle; identifying at least onefirst region of highest stress on the hot weld seam associated withinflation of the bladder without full venting; identifying at least onesecond region of lowest desired restraint force based on interactionbetween a deployment trajectory of the front trim wall and a desiredrestraint profile for a corresponding passenger; placing a stress reliefvent on the bladder member juxtaposed with the first region and having afirst aperture area; and distributing a plurality of tuning vents alongthe hot weld seam wherein the tuning vents are concentrated at thesecond region, wherein the tuning vents each has a respective initialaperture area less than the first aperture area.
 2. The method of claim1 wherein the relief vent and tuning vents are distributed along theouter perimeter of the bladder member so that every arc of 90° of theouter perimeter includes at least one vent opening.
 3. The method ofclaim 1 further comprising the steps of: testing an actual restraintprofile using the respective initial aperture areas; comparing theactual restraint profile with the desired restraint profile to determinea mismatch; and increasing selected ones of the respective initialaperture areas to reduce the mismatch.